Plastic stretch wrapping machines are well known in the art and are covered by numerous patents regarding their structure and operation. An important feature of many of these machines relates to the vertical movement of the plastic film supply, so that large loads can be completely wrapped with stretchable plastic film. It is not uncommon to have the film supply travel to a height of as high as 120 inches. Since many of the machines which include this feature are semi-automatic, there is a great likelihood that an operator of the machine will be working nearby or under the carriage which holds the film supply during operation or temporary shutdown of the machine. For examples, the machine may be stopped temporarily to adjust the wrapping of the load or to replace a spent film supply roll.
This presents a significant safety problem because the carriage assembly can weigh between 40 and 300 pounds and on most occasions, rests at a significant height above the base when the operation of the wrapping apparatus is temporarily discontinued. In the event of a mechanical breakage of the height regulating mechanism (i.e., breakage of the elevating chain, or disconnection of the chain drive means from the drive sprocket or motor), the entire carriage assembly can come crashing down to the base of the unit. Thus, those working around the machine must be careful to avoid having this weight fall on their body, in particular their toes, fingers, or head.
While it is possible to design the stretch wrapping machine with gates or other safety mechanisms to prevent personnel from occupying the space beneath the film supply carriage, such safety devices encumber the proper operation of the machine and also make it much more difficult to easily obtain the required and necessary stretch wrapping of the load.
Therefore, the present invention provides a safety device and method for preventing falling of the carriage in the event of a failure of the height regulating mechanism.